In communications networks, it may be challenging to obtain good performance and capacity for a given communications protocol, its parameters and the physical environment in which the communications network is deployed.
For example, increase in traffic within communications networks such as mobile broadband systems and an equally continuous increase in terms of the data rates requested by end-users accessing services provided by the communications networks may impact how cellular communications networks are deployed. One way of addressing this increase is to deploy lower-power network nodes, such as micro network nodes or pico network nodes, within the coverage area of a macro cell served by a macro network node. Examples where such additional network nodes may be deployed are scenarios where end-users are highly clustered. Examples where end-users may be highly clustered include, but are not limited to, around a square, in a shopping mall, or along a road in a rural area. Such a deployment of additional network nodes is referred to as a heterogeneous or multi-layered network deployment, where the underlying layer of low-power micro or pico network nodes does not need to provide full-area coverage. Rather, low-power network nodes may be deployed to increase capacity and achievable data rates where needed. Outside of the micro- or pico-layer coverage, end-users would access the communications network by means of the overlaid macro cell.
Backhauling based on the Long Term Evolution (LTE) telecommunications standards may be carried either over normal IMT-bands, e.g. the 2.6 GHz frequency band, or by running LTE baseband communications on higher radio frequencies, such as in the 28 GHz frequency band. LTE based backhauling implies that the pico network nodes are connected to a client node which is used to create a wireless link to a hub node.
In any of the above two cases, the wireless links are typically managed by LTE core control mechanisms. For example, the LTE Mobility Management Entity (MME) may be utilized for session control of the LTE links, and the Home Subscription Service (HSS) may be utilized for storing security and Quality of Service (QoS) characteristics of the wireless links individual end-user terminals embedded in the pico network node.
Moreover, in practice more than one client node may connect to a common hub node. This implies support for Radio Resource Management (RRM) functions, such as scheduling and prioritization of the traffic to and from the different clients, at the hub node.
To each client node there might be several pico network nodes, each of which may offer one or several different radio access technologies, such as based on the Universal Mobile Telecommunications System (UMTS), LTE, or IEEE 802.11x to the end-user terminals of the end-users. Therefore there is a need to differentiate between the corresponding backhaul traffic to different nodes in the communications network. For example, any LTE compliant traffic may need to end up in nodes such as the serving gateway (SGW) or the MME and any WiFi compliant traffic may end up in an edge router or an Evolved Packet Data Gateway (ePDG).
Moreover, for a given radio access technology (RAT), QoS differentiation is provided to the end-users (i.e., to the end-user terminals of the end-users) so that e.g. guaranteed bitrate (GBR) services, such as voice calls, will not be disturbed by best effort (BE) services, such as web browsing. In order to enable this, QoS differentiation is needed also on the backhaul links.
If the wireless backhaul is based on LTE, there are tools that provide both the routing functions and QoS differentiation, such as based on the LTE bearer concept. Typically then, for each type of RAT, one GBR and one BE bearer are established on the backhaul links. Different frameworks may be used to prioritize between different traffic, for example to determine if 10 Mbit/s Voice over Internet protocol (VoIP) data to/from one end-user terminal is more or less prioritized than 100 Mbit/s web-surfing data to/from another end-user terminal.
In situations with low traffic, the peak-bitrate provided/offered to the end-user terminals may be limited by the peak-bit rate of the backhaul link. In situations with high traffic load, the maximum capacity for each client node can be limited by the wireless backhaul link due to (interference and) several client nodes sharing the same sector of a hub (i.e., the same hub sector). This implies a decrease in the maximum capacity which a pico network node can provide/offer the end-user terminals.
Since the traffic load pattern might change, the need for a certain backhaul capacity may change over time. In some cases, a hub sector may be able to provide several client nodes with sufficient backhaul capacity, whilst in other cases with more traffic load (or interference conditions), the backhaul link will define the limiting factor of the throughput for the end-user terminals. Hence, the client nodes connected to hub sectors which experience a backhaul limitation as described above will experience fluctuations in throughput depending on the momentary traffic load among the served client nodes, thus making it more difficult to guarantee the end-user terminals a certain throughput.
A similar situation occurs in a case the traffic of a client node is causing interference to other hub sectors than the hub sector serving the client node. Any such negatively affected hub sectors may have a severely limited maximum capacity of its backhaul link. This implies a decrease in the maximum capacity which a client node can provide/offer the end-user terminals.
In the above described cases, one common issue is that even though the individual wireless backhaul links are good (e.g., providing/offering high bitrate), the throughput is likely to be lower if the wireless backhaul links are shared and/or interfered.
Hence, there is still a need for an improved handling of wireless links in a wireless backhaul network.